Courses taught:

Professional Affiliations:

Current and Past Research Projects:

A macrosystems ecology framework for continental-scale prediction and understanding of lakes

In the past decade, our understanding of how inland waters influence regional, continental, and global biogeochemical cycles has fundamentally changed. We have moved from discounting their contributions, to now recognizing these ecosystems as significant hotspots for the storage and transformation of nitrogen, phosphorus, and carbon. This realization has come about through careful and labor-intensive collection, integration, and synthesis of often-scattered data sources, combined with a variety of different approaches to extrapolate site-level measures to unsampled sites across regions and continents. Today, although this view of the role of inland waters in large-scale cycling is supported by numerous studies, substantial gaps in our understanding remain. Estimates for the same flux (e.g., organic carbon burial in lakes) often differ substantially among studies. Further, most attempts to quantify continental or global fluxes or pools come with caveats regarding the often high– and often unknown– uncertainty associated with these estimates. To better understand the role of inland waters in macroscale nutrient cycling, new approaches are needed to reduce uncertainty in extrapolating site-level estimates to larger geographical scales. The overarching goal of this NSF-funded research is to understand and predict nutrient patterns for ALL continental US lakes to inform estimates of lake contributions to continental and global cycles of nitrogen (N), phosphorus (P), and carbon (C), while also providing locally valuable information about conditions in unsampled lakes.

Establishing a strategy for assessing the risk of endocrine-disrupting compounds to aquatic and terrestrial organisms

Endocrine disruption is a national and global concern that affects fish, wildlife and human populations. Through interactions with neural, endocrine, and immune systems, endocrine disrupting compounds (EDCs) can influence growth, development, reproduction, disease, and mortality, with adverse outcomes for populations, communities, and ecosystems. Within the Chesapeake Bay, understanding the effects of EDCs on fish and wildlife populations has been identified as a priority to help inform natural resource management. Specifically, there is a need for assessing the risk of EDCs to fish and wildlife populations and their health. The risk assessment will integrate our understanding of the (1) population dynamics of the fish or wildlife species of interest, (2) mechanisms through which EDCs interact with individuals, and (3) exposure pathways between sources of EDCs, including hydrological conditions and land use practices, and fish and wildlife populations. This will help identify short and long-term impacts of compounds or classes of chemicals of concern, potential environmental conditions and stressors that may mediate the effects of EDCs, and how land use management practices may reduce exposure to EDCs.

Linking fish health, contaminants, and population dynamics of smallmouth bass populations in the Susquehanna River, Pennsylvania

Since 2005, diseased smallmouth bass have been detected throughout the Susquehanna River and its tributaries raising concern regarding the overall health of smallmouth bass and the Susquehanna River basin. In a collaborative effort with Pennsylvania Fish and Boat Commission, PA Department of Environmental Protection, U.S. Geological Survey, and Penn State University, this project aims to investigate a wide-range of variables (i.e., fish health analysis, contaminants, population modeling, radio telemetry, etc.) to gain a better understanding of factors that could relate to disease in smallmouth bass.

An investigation into the role of groundwater as a point source of emerging contaminants to smallmouth bass in the Susquehanna River basin

There is currently a paucity of information on the role of groundwater discharge into surface waters as point sources of contaminants from polluted aquifers. This is critical to understand because the use of groundwater seeps are important for smallmouth bass, particularly during spawning season, and there use is related to increased hatch success and survival of age 0 fish. In addition, previous work has shown smallmouth bass utilizing areas of groundwater upwelling for spawning in the Susquehanna River basin. Exposure to EDCs during this critical life-stage of egg development could have detrimental short- and long-term consequences on immune function and fish health. Therefore, the objective of this research is to investigate the role of groundwater as a point source of emerging contaminants to smallmouth bass in the Susquehanna River basin.

Rates of population extirpation from habitat loss have reached unprecedented levels and climate change is predicted to be a leading cause of future species extinctions. Accordingly, conservation of emergent properties that promote resistance and resilience to environmental perturbation will be vital to future population persistence. Though it has been demonstrated that phenotypic plasticity increases resilience to habitat loss, the ability for plasticity to promote population persistence under climate change and habitat degradation has not been explored. If plasticity does increase survival, failure to conserve highly plastic genotypes could accelerate species extinction. This research focuses on an economically and socially important species, brook trout (Salvelinus fontinalis), to determine how the interactive effects of genetics and behavior influence differential survival of fish populations under a changing climate.

Preliminary determination of density and distribution of Flathead Catfish Pylodictis olivaris in the Susquehanna River and select tributaries

The goal of this project is to estimate the relative abundance and age and growth characteristics of invasive Flathead Catfish in three reaches of the mainstem Susquehanna River with different degrees of population establishment. By examining river reaches with different degrees of population establishment, data collected during this study will serve to help understand current distribution and population characteristics (e.g., size distribution, growth rates). In addition, we will develop models (based on population vital rates and habitat use) to predict future changes in establishing populations as well as to evaluate potential impacts to areas where Flathead Catfish have not yet invaded. These models can be used to help inform management of Flathead Catfish and native species throughout the Susquehanna River Basin.

Macrosystems biology research in US lakes across space and time

As part of a dynamic multidisciplinary research team (http://csi-limnology.org/), we seek to identify and study cross-scale interactions (CSIs) at sub-regional to continental scales. A CSI exists where a driver at one scale, such as local land use, interacts with a driver at another scale, such as regional climate. These CSIs can lead to nonlinear and often unexpected relationships between drivers and responses.

A central challenge to natural resource management is to understand and predict ecological responses to management and environmental change over large spatial scales. It is recognized, however, that the management and conservation of many important ecological systems and the services they provide must be addressed at spatial scales that transcend jurisdictional and political boundaries. For example Landscape Conservation Cooperatives (LCCs) recognize that managing natural resources is complex and requires landscape-scale (i.e., trans-boundary) approaches. Although trans-boundary approaches are necessary to understand large-scale phenomenon (e.g., species range), it remains unclear in many cases how best to address the inherent complexities in managing ecosystems at large (e.g., regional) spatial scales. In addition to challenges associated with performing trans-boundary research, it is often unclear how to link large-scale system dynamics with on-the-ground decision-making processes, which are often done using adaptive management principles. For example, a critical component for successfully implementing adaptive management is the development of a rigorous monitoring program, which provides a critical feedback loop for learning about system dynamics. It is unclear, however, how the interplay between components acting at different, hierarchical scales will affect the ability of natural resource managers to detect changes in important state variables (e.g., animal abundance, occupancy, etc.) at trans-boundary spatial scales. Thus, our overarching objective is to use freshwater stream fish populations as model systems to develop a framework and tools for addressing the inherent challenges in performing trans-boundary research and for linking large-scale dynamics to ecological monitoring and management.

Great Lakes Fisheries Trophic Structure Response to Climate Change

Predicting population responses to climate change requires an understanding of how population dynamics vary over space and time. Although variability has historically been viewed as an impediment to understanding population responses to ecological changes, it can provide an important signal, rather than just being viewed as noise. In this project, we will build upon recently completed analyses of fish population data in the Great Lakes basin to help predict how spatial and temporal variation in fish populations may respond to climate change and other important drivers. We suggest that shifting variance structure can be indicative of population-level responses to climate change. Our proposed research will help elucidate the extent to which quantifiable responses in spatial and temporal variability occur in different forms of fish population data.

Fish Community Assessment in the Eastern Rivers and Mountains Network and Integration with Existing Monitoring Data

The National Park Service (NPS) has initiated a long-term ecological monitoring program, known as “Vital Signs Monitoring”, to provide the minimum infrastructure to allow more than 270 national park system units to identify and implement long-term monitoring of their highest-priority measurements of resource condition. The Eastern Rivers and Mountains Network (ERMN) includes nine parks in New York, New Jersey, Pennsylvania, and West Virginia which together encompass nearly 91,000 ha of land area and more than 600 stream and river miles within the parks’ authorized boundaries. A primary objective of the ERMN monitoring program is to evaluate status and trends in the condition of tributary watersheds flowing into and through member parks. Currently, the monitoring of fish communities is not part of the monitoring program. Consequently, methodology is needed to estimate the current condition of fish communities in ERMN wadeable streams in a rigorous and repeatable manner. Estimates of the current fish community’s condition at ERMN stream sites will complement data collected on an annual basis (i.e., Vital Signs Monitoring) and enable an integrated measure of ecosystem condition that can be monitored over time. The specific objectives of this study are to: (1) characterize fish communities in selected ERMN stream reaches, and (2) combine fish community data with existing monitoring data (e.g., macroinvertebrates) to provide an integrated measure of stream ecological condition.

DeWeber, J.T. and T. Wagner. 2015. Translating climate change effects into everyday language: an example of more driving and less angling. Fisheries 40:395-398.

DeWeber, J.T and T. Wagner. 2015. Predicting brook trout occurrence in stream reaches throughout their native range in the eastern United States. Transactions of the American Fisheries Society 144:11-24.

Wagner, T. and J.A. Sweka. 2011.Evaluation of hypotheses for describing temporal trends in Atlantic salmon parr densities in Northeast U.S. Rivers. North American Journal of Fisheries Management 31:340–351.

Wagner, T., C.S. Vandergoot, and J. Tyson. 2009. Evaluating the Power to Detect Temporal Trends in Fishery-Independent Surveys: A Case Study Based on Gillnets Set in the Ohio Waters of Lake Erie for Walleye. North American Journal of Fisheries Management 29:805-816.